The present invention relates generally to semiconductor wafer treating apparatus such as thermal processing machines, and more particularly to pin-type wafer holders used to support semiconductor wafers during treatment in wafer treating apparatus.
Prior art pin-type holders comprise three pins, each of which has an upper end for supporting a bottom surface of the wafer. Three pins are conventionally used since the three upper ends constitute three points which define a plane. Using more than three pins to hold the wafer is more difficult since it is difficult to align more than three points (i.e., points defined by upper ends of the pins) in the same plane. Moreover, the bottom surface of the wafer may not be perfectly planar, so that even if the pins are aligned, they may not all contact the wafer.
A typical use of a wafer holder is to support the wafer in a thermal processing machine. The wafer deforms during thermal processing such that portions of the bottom surface of the wafer are forced against the pins. Such motion creates damage on the bottom surface of the wafer and results in dislocations which may propagate through the wafer and negatively affect the front surface of the wafer. Such damage is increased as the weight of the wafer is increased. In conventional three-pin holders, each pin must support one third of the weight of the wafer. Wafer consumers now demand larger diameter wafers which are heavier, and the damage caused by the three pin holders is thereby worsened.
Another type of holder uses a combination of fixed pins and spring biased pins, as shown in U.S. Pat. No. 5,718,574. However, such an arrangement is not desirable since the wafer will be damaged by the fixed pins, and because the weight of the wafer may not be evenly distributed among the pins.
Among the several objects and features of the present invention may be noted the provision of a semiconductor wafer holder which inhibits damage and dislocations in the wafer, the provision of such a holder which decreases the number of wafers damaged during thermal processing, and the provision of such a holder which increases the yield of acceptable wafers.
Briefly, apparatus of this invention is a holder for holding a semiconductor wafer for treatment in wafer treating apparatus including a plurality of supports for generally point support of the wafer at a plurality of points on the wafer. Each support bears a fraction of weight of the wafer and is movable up and down and subject to force biasing it to move upward. The total of the forces exerted on the supports biasing them upward is adapted to counterbalance the weight of the wafer.
In another aspect of the invention, the holder comprises a plurality of wafer rests for the resting of the wafer thereon. Each rest is extensible up and down and comprises a lower elongate member fixed in generally vertically extending position. Each rest further comprises a generally vertically extending cylinder constituting a wafer-holding pin including a lower end slidable up and down on the lower members and an upper closed end having a tapered tip for generally point engagement with a bottom surface of the wafer. The cylinders provide at their upper ends for generally point support of the wafer at a plurality of points distributed around the bottom of the wafer. Each cylinder bears a fraction of the weight of the wafer. The holder further comprises a system for flow of gas under pressure into and out of each cylinder for establishing an upwardly biasing force on each cylinder. The total of the forces exerted on the cylinders biases them upward and is adapted to counterbalance the weight of the wafer.
In yet another aspect of the present invention, the holder comprises a plurality of wafer rests which are extensible up and down. Each rest comprises an upper member having an upper end for resting thereon of the wafer. Each upper member is movable up and down on a fixed lower member. The upper members provide at their upper ends for generally point support of the wafer at a plurality of points. Each upper member bears a fraction of weight of the wafer and is subject to force biasing it to move upward relative to the fixed lower member. The total of the forces exerted on the upper members biasing them upward is adapted to counterbalance the weight of the wafer.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.